This invention relates to a shutter curtain for a single lens reflex camera.
In recent years "systematization" has been a notable trend in the continuing development of single lens reflex cameras, as evidenced by exchangeable finders, lens attachments, increased functional adaptability, etc. As a result the construction of such cameras, including their light measuring optical systems and circuitry, has become more complicated, as with the advent of automatic exposure control which affords added handling ease to camera users. The location of the light sensing element(s) in a SLR camera, on the other hand, which is a prerequisite to any TTL light measuring system, varies widely between different cameras, with each location having certain advantages and disadvantages.
There are two basic light sensing element locations in common use; one in which the element is disposed at the periphery of the penta prism, and another in which the element is disposed in the lower portion of the mirror box, on the periphery of the focusing plate, or on the periphery of the reflex mirror.
The former type is advantageous in that the field of view in the finder is not impaired, and the light measuring and optical functions are comparatively standardized between cameras of different manufacturers. This type involves drawbacks, however, particularly with systematized, exchangeable finder cameras wherein electrical connections to the camera body must be made and different light sensing elements must be provided in each type of finder. In addition, when a given focusing plate is exchanged for another one some degree of exposure compensation must usually be made.
The type wherein the light sensing element is disposed in the lower portion of the mirror box functions independent of finder or focusing plate exchanges, however, and thus does not interfere with the systematization or automatization of the camera. It is accordingly an object of the present invention to provide an improved shutter curtain for a SLR camera of this type, wherein the measurement characteristics of light reflected by the plane of the shutter curtain are greatly improved.
Among the various light measuring characteristics of a fully open, T.T.L. single lens reflex camera, the most significant are:
(1) The ability of being interlockable with a lens diaphragm or aperture, PA1 (2) The distribution of received light, and PA1 (3) The light sensing efficiency.
In designing a camera light measuring system, heavy consideration must be given to these three characteristics.
Various shutter curtains are used in SLR cameras, with rubber lined cloth curtains and metallic (titanium) curtains being the most prevalent. Because such rubber lined cloth and metallic curtains fail to satisfy the aforesaid three characteristics of a light measuring system, however, particularly the distribution of received light and the light sensing effeciency, they must be modified or adapted in some way. The most prevalent method is to secure a reflecting substance or layer to the surface of the shutter curtain by adhesive coating or printing, but shutter curtains subjected to such processes are likely to undergo qualitative changes during prolonged usage, and hence lack long term reliability.